1. Field of the Invention
The invention relates to a fuel injection valve with a nozzle needle which is guided in a central guide bore of a nozzle body and has a peripheral sealing region having a sealing edge which, together with the valve seat of the nozzle body, forms a valve which is opened or closed, depending on the position of the nozzle needle, and controls the inflow of fuel to at least one injection hole in the nozzle tip of the nozzle body.
In injection systems, fuel is injected under high pressure into the combustion space of an internal combustion engine via a fuel injection valve.
2. Description of the Related Art
WO 96/19661 discloses a fuel injection valve having a nozzle body with a central guide bore, in which a nozzle needle is guided. The valve opens as a result of the axial movement of the nozzle needle, said valve being formed by the sealing edge of the nozzle needle and the conical valve seat at the nozzle tip of the nozzle body. The valve thus controls the flow of fuel to the injection holes which are introduced into the nozzle tip. A step in the form of a peripheral groove is introduced below the sealing edge of the nozzle needle, in order to prevent the change in the valve seat diameter which is caused by wear.
When the valve closes, the sealing edge of the nozzle needle strikes the conical valve seat sharply, thus giving rise to pronounced mechanical stress on the nozzle body which may lead to a curtailed service life of the latter.
The object of the invention is to reduce the mechanical stress on the nozzle body which occurs during the closing of the valve.
The object of the invention is achieved by means of the features of the independent patent claim.
Advantageous embodiments of the invention are specified in the dependent claims.
In the invention, the nozzle needle has, between its frustoconical nozzle needle tip and its cylindrical needle shank, a frustoconically designed body portion which, at its transition to the nozzle needle tip, has a sealing edge which, together with the conical valve seat of the nozzle tip of a nozzle body, forms a valve. The conical valve seat forms, with the frustoconical body portion of the nozzle needle, an angle the sides of which meet at the sealing edge and which forms a small angle in the region of a few degrees. During the closing of the valve, that is to say when the sealing edge strikes the conical valve seat, the fuel in the gap between the body portion of the nozzle needle and the conical valve seat is pressed out, with the result that the closing action is damped.
The peripheral gap between the valve seat and the body portion is partially enlarged by means of a recess in the nozzle needle or in the nozzle body, with the result that the effect of damping the closing action can be set. The recess is designed as a peripheral groove in the nozzle needle or in the nozzle body. The damping effect can be set, depending on the position of the recess, that is to say on the axial position of the recess and on the size of the recess.
In one embodiment, the peripheral groove is made directly at the sealing edge of the nozzle needle, with the result that, in addition to the damping effect, the valve seat diameter does not change, or changes only insignificantly, when the nozzle needle undergoes wear at the sealing edge.
In a further embodiment, a frustoconical body portion of the nozzle needle is arranged between the peripheral groove and the sealing edge, as a result of which the damping effect can be set, depending on the axial length of this body portion.
In a further embodiment, the peripheral groove has a first and a second groove portion which is arranged in the direction of the sealing edge or of the shank bore, the first groove portion being of cylindrical design. This makes it possible to manufacture the groove in a simple way within the respective body portion of the nozzle needle. Additionally, when the cylindrical second groove portion is arranged directly at the sealing edge, the effect of wear on the valve seat diameter is only slight.
Furthermore, the recess is introduced as a peripheral groove into the inner wall of the valve seat of the nozzle body.
In a further embodiment, a further peripheral groove is introduced into the frustoconical nozzle needle tip and serves for guiding the nozzle needle radially during the opening and closing of the valve.
The nozzle body is advantageously designed in the form of a seat hole nozzle, the injection holes of which are located in the region of the conical valve seat.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a fuel injection valve for an internal combustion engine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.